This will allow us to add an option to disable the screensaver on the client
when an application in the guest requests it. This behaviour may be useful
when the guest is doing media playback.
Instead of using %windir%\Temp, which is not accessible by default and
contains a lot of unrelated files, as the location for our log files,
this commit moves it to %ProgramData%\Looking Glass (host), which will
be a dedicated directory just for the LG host log files. This applies
to both the host application logs and the service logs.
Also, we now switched to using PathCombineA from shlwapi.dll instead
of using snprintf, which greatly simplifies the code. PathCombineA
guarantees that the path would not overflow a buffer of MAX_PATH.
Before this commit, the NvFBC backend only generated the first cursor
position update when the mouse moves. Therefore, if the user does
not move the mouse, the cursor will be shown at (0, 0), which is not
ideal.
This commit changes this behaviour to unconditionally generate a
cursor update when the mouse hook initializes.
Before this change, the log is buffered, so if the host application exits
for any reason, it usually would not show up in the log file immediately,
and the service has to be restarted for the logs to be flushed.
This commit disables the buffering so that any log entries shows up
immediately.
NvFBC is unable to capture certain applications that bypasses the DWM
compositor, for example, Firefox playing video in full screen. This
has been a known issue for a long time with Nvidia's ShadowPlay, see:
* https://www.nvidia.com/en-us/geforce/forums/geforce-experience/14/233709/
* https://crbug.com/609857
Nvidia won't fix this, but there are workarounds. For example, we
create a transparent 1x1 layered window, which forces desktop composition
to be enabled.
Note that SetLayeredWindowAttributes also supports alpha-based transparency,
but setting transparency to 0 will cause DWM to skip composition. We could
use a transparency of 1, but this ruins the image by the slightest bit,
which is unacceptable. Therefore, we must use chroma key-based
transparency, which tricks DWM into compositing despite being fully
transparent.
Basically, this creates a separate thread for the mouse events, and this
thread detects that the desktop has changed (say to the secure desktop),
and unhooks, switches to the new desktop, and then rehooks.
This allows the cursor location to be updated while using NvFBC on secure
desktop and the login screen.
WTSGetActiveConsoleSessionId will return a session even if it's not logged in,
unlike our old GetInteractiveSessionID function. Launching looking glass on
such a console session will allow the login screen to be captured.
Note that WTSGetActiveConsoleSessionId() will return 0xFFFFFFFF if there are
no sessions attached.
To quote MSDN documentation:
> The lpApplicationName parameter can be NULL, in which case the executable
> name must be the first white space–delimited string in lpCommandLine. If
> the executable or path name has a space in it, there is a risk that a
> different executable could be run because of the way the function parses
> spaces. The following example is dangerous because the function will
> attempt to run "Program.exe", if it exists, instead of "MyApp.exe".
>
> LPTSTR szCmdline[] = _tcsdup(TEXT("C:\\Program Files\\MyApp"));
> CreateProcessAsUser(hToken, NULL, szCmdline, /*...*/ );
>
> If a malicious user were to create an application called "Program.exe" on
> a system, any program that incorrectly calls CreateProcessAsUser using the
> Program Files directory will run this application instead of the intended
> application.
>
> To avoid this problem, do not pass NULL for lpApplicationName.
So instead, we pass the executable to lpApplicationName instead, which avoids
the issue. MSDN says:
> The lpCommandLine parameter can be NULL. In that case, the function uses
> the string pointed to by lpApplicationName as the command line.
This also avoids the strdup since lpApplicationName is LPCSTR unlike
lpCommandLine which is LPSTR.
It shouldn't have any effect, since the host application is created with
the token, and there is no need for the service itself to impersonate.
In practice, removal doesn't appear to have any effect on the ability to
capture privileged things like secure desktop.
Use the process handle returned by CreateProcessAsUserA to wait on the
process. This results in faster response times and less polling.
For example, it now restarts instantly when UAC is activated.
This also removes the call to OpenProcess and rendering the mutex unnecessary.
As a bonus, it should fix#298.
The host process will be changed to return these codes, from which the
service process could decide whether to exit or restart the process and log.
Note that on Windows, return values are 32-bit unlike POSIX which is only 8.
This makes it a compile-time error to call a function that semantically
takes no parameters with a nonzero number of arguments.
Previously, such code would still compile, but risk blowing up the stack
if a compiler chose to use something other than caller-cleanup calling
conventions.
Now that it's recommended to run LG as the `SYSTEM` user, launching an
application to read the log file is dangerous as it will be launched
with the same access rights (`SYSTEM`). Instead so as Microsoft
recommends and only present a message box with the information.
Experimental, use at your own peril!
This commit adds the ability for the LG host to install and launch with
Windows as a system service.
To install simply run `looking-glass-host.exe InstallService` or
conversely to uninstall `looking-glass-host.exe UninstallService`.
